Sweet potatoes (Ipomoea batatas), members of the morning glory family, are grown from sprouts called slips. Be sure to order slips from a source that offers certified disease-free stock, because slips have been known to carry harmful diseases, including black rot. (We’ve listed reliable sources further down the page.) Planting and growing sweet potatoes is straightforward, but we’ve gathered these tips to make sure you get a sweet harvest next year:
Choose the right variety of sweet potato
Heirloom varieties taste better than more recent introductions, says Glenn Drowns, who grows 86 sweet potato varieties at the Sandhill Preservation Center in Calamus, Iowa. Drowns’ favorites are ‘Betty’s’, ‘Frazier White’, and ‘Ivis White Cream’. But those may not be the best choices for your garden. If you live in a cool-season climate, select a short-season variety (see “Cool-Season Tricks” below for specifics). In the South, plant a mixture of short- and long-season varieties and you can harvest sweet potatoes for several months. If you or other gardeners in your area have had problems with diseases affecting sweet potatoes, you can solve that the organic way by choosing resistant varieties. Root-knot nematodes and fusarium wilt, for instance, are prevalent in many areas of the South. ‘Excel’ (with orange flesh), ‘Jewel’ (deep orange), ‘White Regal’, and ‘Topaz’ resist these plagues. If you have very limited space, try a bush variety, such as ‘Porto Rico’ (light red) or ‘Vardaman’ (red orange).
Rotate the crop
“The most important thing gardeners should do is rotate,” states Danielle Treadwell, Ph.D., an organic and sustainable farming specialist at the University of Florida. Plant sweet potatoes in a different location every year to discourage wireworms, which will bore into the tubers and blemish them cosmetically (though they are still edible), and diseases such as black rot and scurf, which cause postharvest rotting. Don’t use the same space for sweet potatoes more than once every four years. If you have a small garden, consider growing them in containers and changing the soil each year.
Feed your soil
Grow cover crops—“green manure” plants that add organic matter and nutrients to your soil—to feed your sweet potatoes gently and steadily without additional fertilizers. The tuberous roots need no more nitrogen than is supplied by legume cover crops, such as field peas, says Treadwell. Mix seeds of a winter annual legume (field peas) with a cereal grain such as oats or rye. A 1-to-3 ratio of peas to grain will deliver enough, but not too much, nitrogen. Plant in fall, and when the legume blooms, mow down the cover crop and turn it 8 inches into the soil. This combination slowly releases nutrients into the soil, Treadwell says. Get a soil test to determine if you need to add other essential nutrients, such as phosphorus and potassium, or adjust your soil pH. “Sweet potatoes thrive where the pH is 5.6 to 6.5,” says Rosie Lerner, a consumer horticulture specialist at Purdue University.
If you’re not ready or able to grow cover crops in your garden, spread a 2-to-3-inch layer of finished compost on the bed where you want to plant sweet potatoes. Gently scratch the compost into the top 6 inches of soil before planting. The compost will nourish your sweet potatoes, balance the soil pH, discourage diseases, and help with moisture management. (How’s that for multitasking?)
Sweet potatoes grow best in warm soil and hot weather, Drowns says. Mound the soil in your bed into ridges. This helps heat up the soil in spring and also allows rainwater to drain away, protecting the tubers from rotting. Mound ridges two weeks before planting—18 inches wide and 10 inches high on light soils, 12 inches wide and 15 inches high on heavier soils. Allow 3 feet between rows.
Leave space between. Plant slips on the top of mounds, burying them up to their first set of leaves. Space plants 12 to 18 inches apart. Keep slips consistently moist for a week after planting.
Mulch the mounds
Cover the soil with mulch to conserve moisture and discourage weeds. In the North, laying black plastic mulch on the ground a week or two before planting is an effective way to warm the soil. To plant the slips, poke a hole in the plastic and set the plant in the hole. Mulch also helps produce bigger sweet potato yields by preventing the plant from rooting at spots where the vine and soil meet. These side roots draw energy away from root production on the main plant, Drowns explains. In southern zones, mulch protects plants from the sweet potato weevil (Cylas formicarius), a widespread pest that gains access to the roots through cracks in dry soil.
Harvest after frost
“Remove the vines and dig immediately after the first light frost,” says Richard de Wilde, of Harmony Valley Farms in Viroqua, Wisconsin. Cure sweet potatoes for about three weeks in a warm, humid location, such as your kitchen. After curing, store sweet potatoes in a dark spot at moderately cool temperatures (55° to 60°F). Healthy roots that have been cured and stored properly can last four to six months in storage.
Where to Order Sweet Potatoes
Irish Eyes–Garden City Seeds, Thorp, WA; 509-964-7000, irish-eyes.com
Miller Nurseries, Canandaigua, NY; 800-836-9630, millernurseries.com
Sand Hill Preservation Center, Calamus, IA; 563-246-2299, sandhillpreservation.com
Steele Plant Company, Gleason, TN; 731-648-5476, sweetpotatoplant.com
Sweet potatoes need about four frost-free months to mature. If your growing season is shorter than that, you don’t have to give up on growing your own sweet potatoes. With one or all of these strategies, you can harvest your own sweet potatoes no matter how far north you live.
Start with a short-season variety. Try an heirloom proven in short seasons, such as ‘Frazier White’, ‘Continental Red’, or ‘Ivis White Cream’, or the more widely available ‘Centennial’.
Use plastic mulch. Cover your sweet potato mounds with black plastic two to three weeks before you plant—the soil temperature beneath the plastic is typically several degrees warmer than uncovered soil. When you are ready to plant, leave the plastic in place and cut slits in it through which you will put in your slips.
Don’t rush planting. Researchers at North Carolina State University found that sweet potatoes grow faster when planted later. “Even if you have a short season, you’re far better off waiting until the early part of June to plant,” says Glenn Drowns, a seed saver and sweet potato preservationist in Iowa.
Grow in containers. Sweet potatoes produce well in large containers such as whiskey barrels. Remember that they need to be well watered and fertilized regularly. (Use an organic liquid fertilizer, such a fish-and-seaweed mix, which is rich in micronutrients as well as the major ones.)
Extend the season. When the first light frosts of fall threaten to end your sweet potato season, you can keep them growing a bit longer by bringing containers inside or covering the plants with old sheets or blankets.
Fresh sweet potato sensations
Bob Perry serves a lot of sweet potatoes—not because he makes Thanksgiving dinner for a large family, but rather because he’s the director of food service and executive chef for the Kentucky Department of Parks. Perry’s mission is to offer visitors to the parks’ 21 restaurants an authentic taste of the region by serving food grown on local farms. (He developed his passion for locally grown ingredients while he was training to be a chef in the south of France.)
Roasting is Perry’s favorite way to prepare sweet potatoes. “It concentrates the sugars within the sweet potato,” he says. “I would never boil a mature, cured sweet potato.” His Mad Dog Sweet Potatoes are flavored with Kentucky bourbon and sorghum syrup. “Sorghum is the country syrup,” he says. “Wherever I have traveled as a professional chef, I have tried to take a little bit of Kentucky with me. Bourbon and sorghum are two easy ways to do this.”
While you’re dreaming of next season’s sweet potato crop, try these simple but delicious ways to prepare and serve them this year:
Bake. Preheat the oven to 350°F. Poke each tuber with a fork and bake until tender (about one hour). Top with butter, margarine, brown sugar, cranberries, salsa, sour cream, or honey, suggests Sue Johnson-Langdon, of the North Carolina Sweetpotato Commission.
Mash. Steam, bake, or roast the sweet potatoes. Meanwhile, sauté chopped onion, garlic, medium-hot peppers, and cilantro. Add the onion mixture to the cooked sweet potatoes and mash. Use as a filling for tacos, burritos, and enchiladas.
Microwave. In a hurry? Poke one sweet potato with a fork and microwave on high for 4 to 6 minutes or until it’s tender, turning it over halfway through cooking. Research at New Zealand’s University of Auckland indicates that microwaving better preserves the skin’s healthful antioxidants. For the best flavor fast, Louisiana State University Agricultural Center dietitian Beth Reames suggests baking sweet potatoes about a half hour in a conventional oven, then finishing to taste in the microwave.
Steam. “When a recipe calls for boiled sweet potatoes, I steam or roast them,” writes Dana Jacobi in the 12 Best Foods Cookbook. “Steamed, they hold their shape, while boiling makes them taste watery and turns them to mush.” Peel and dice the tubers into 1/2-inch chunks. Steam until tender (about 5 or 6 minutes). Serve with melted butter and a dusting of nutmeg.
Roast. Preheat the oven to 500°F. Cut the sweet potatoes into wedges or cubes, toss with olive oil, and spread in a shallow roasting pan. Roast for 15 to 20 minutes. Shake the pan occasionally for even browning.
Bob Perry’s Mad Dog Sweet Potatoes
3–4 sweet potatoes, or about 3 pounds
1 tablespoon vegetable oil
1/2 cup Kentucky pure sorghum
1/2 stick unsalted butter
Splash of Kentucky bourbon
1 teaspoon kosher salt
1. Preheat the oven to 350°F. Wash the sweet potatoes and rub on a small amount of oil to coat their skins. Place in a baking dish and bake for about an hour like a regular baked potato.
2. Allow the sweet potatoes to cool slightly, then peel and discard the skins and roughly chop. Place in a large mixing bowl and add the sorghum, butter, bourbon, and salt. Mix slowly, then on high speed to blend all ingredients. Turn into a serving bowl and enjoy. You may also top them with marshmallows or pecans. Just reheat in the oven for a few minutes, then broil to brown the marshmallows.
Sweet potatoes are somtimes called yams but yams belong to a different plant family and are native to Asia and West Africa. The sweet potatoes cultivated in North America originated in Peru and Ecuador.
Slaves from Africa found the American sweet potato like their native nyami and introduced one of Southern cuisine's essentials in the plantation kitchens where they cooked.
Americans eat an average of 4 pounds of sweet potatoes per person each year. That's a decrease from 31 pounds in 1920, and it is roughly equivalent to the amount of celery we eat.